Supplying hot water on Shabbat can be a troublesome problem. It is true that taking a hot shower is forbidden, and even if the water is heated before Shabbat one is only allowed to wash "his face and his hands and feet," but there are other needs, such as washing dishes, cleaning babies, and personal needs.
Many institutions (such as hotels, hospitals, dormitories, and kibbutzim) have central heating systems instead of individual boilers in each apartment. These operate on the principle of heat exchange – the water is heated by contact with a metal pipe or wall which in turn is heated by hot water.
In the opinion of The Zomet Institute, if the heat exchanger does not have any heating elements of its own, the water can be considered as being heated in a kli sheini – a utensil that did not have direct contact with a flame – even if its temperature is above what is usually considered so hot that a hand will be scalded (42 degrees C).
See the detailed article written by Rabbi Yisrael Rozen, Techumin, volume 24.
In an institution where the rooms have individual boilers, the same solution can be used as in private homes, based on the method of continuing an existing current.
For consultation and details, contact The Zomet Institute.